Poorly differentiated thyroid carcinoma: an evolving entity

The term Poorly Differentiated Thyroid Carcinoma (PDTC) was first proposed in the early eighties to describe a heterogeneous group of neoplasms, of follicular cell origin, dwelling in an intermediate clinicopathological position between well-differentiated follicular or papillary carcinomas and undifferentiated carcinomas. Over the following two decades defenders and sceptics have sustained an unsurmountable debate pertaining the nature of PDTC, its morphological diagnostic features, its clinical relevance and the most suitable management. In 2004, the WHO Committee on Thyroid Tumours agreed to recognize PDTCs as a distinct entity in thyroid follicular cell tumourigenesis. The proposed diagnostic criteria resulted however difficult to apply on daily practice. Four years ago, in an attempt to streamline the diagnosis of PDTC, a panel of experts met in Turin and developed a simple algorithmic approach for PDTC identification. This paper aims to review the state of the art on PDTC from a morphological, clinical and molecular standpoint.